RE: A85: Re: Z80 Hardware
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RE: A85: Re: Z80 Hardware
The port data (in this case the register contents) appears on the data lines
and the port address is on the address buss just like memory access, except
the IORQ (I/O request) line is strobed instead of MREQ (memory request).
-----Original Message-----
From: Keith Burzinski [SMTP:tsk3000@prodigy.net]
Sent: Monday, September 15, 1997 5:06 PM
To: List-Assembly-85
Subject: Re: A85: Re: Z80 Hardware
> > I'm presently designing a Z80 micro-computer system. But there are a
> > few things I don't really understand yet. ;) Mainly the ports. Like,
> > if I do 'out (7),a', where does that go, and how does it get there???
> > Is it somehow attatched to the address bus? And then it reads the byte
> > on the data bus? How??? Help me! :)
>
> It'll send whatever byte is in register A.
I know this! I need to know _HOW_ the byte in A is written to the
device connected to the port. Is it sent through the data bus?
For example: if I
ld $C0,a
out (7),a
it will write $C0 to the device on port 7 (in this case, the link
port). But _HOW_ is that $C0 _ACTUALLY_ written to the link port???
_WHAT ACTUALLY_ changes the lines on the link port? It can't just be
"wired into the processor". It has to have a line driver of some sort,
and some device to actually READ the byte from the processor. Remember,
SOMETHING has to read it; it just doesn't magically go there... I need
to know, how does that device interface with the Z80 processor chip???
Reguards,
--
~Keith
TSK3000@Prodigy.Net
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